Inhibition par les lipoprotéines de haute densité HDL2 et HDL3 de la synthèse du DNA et des stérols des lymphocytes humains stimulés par la concanavaline A.

Lipoproteins HDL₂ and HDL₃ inhibit DNA synthesis and sterol synthesis in human Con A-stimulated lymphocytes cultured in a medium supplemented with 20 per cent lipoprotein deficient serum. On the basis of the amount of proteins added, HDL₂ is more efficient on DNA and sterol synthesis than HDL₃ and less efficient than LDL. However, on the basis of the amount of cholesterol added, the inhibition of sterol synthesis induced by these three lipoproteins is not significantly different. At all concentrations of these three lipoproteins, the inhibition of sterol synthesis is higher than the inhibition of DNA synthesis.     

Stimulation par l'Œstradiol de la synthèse des ribosomes dans les cellules adénohypophysaires

A single dose of 10 μg oestradiol injected to a male rat stimulates in the anterior pituitary the synthesis of ribosomal RNA and of the associated proteins. This stimulation is shown using in vitro double-labeling of RNA with adenine or guanine and of proteins with valine. The analysis of polysomes reveals the incorporation of the neo-synthesized molecules into the 40 S and 60 S subunits. Therefore, the stimulation of ribosomal RNA and protein biosynthesis by oestradiol is a coordinated process. No change in the whole polysome distribution is observed in these conditions though such a modification may occur in a specific cell population without being detected by using sucrose gradient analysis.     

Action de la 8-azaguanine sur la division cellulaire de Chlorella pyrenoidosa

Summary Synchronized Chlorella cell cultures were supplemented with 8-azaguanine at different times in their life-cycle. The number of cells obtained after one cycle depended on the time at which the analogue was added to the cultures. The results suggest that, during one cycle, the successive cellular divisions are controlled by a specific stimulus.When supplied to the cultures during at least one entire cycle, 8-azaguanine inhibited the replication of the nuclear DNA, whereas satellite DNAs continued to replicate. The possibility of a reversal of the phenomenon by guanosine has been studied.     

Effets du retard dans la première alimentation sur le développement de la larve planctotrophe de l'oursin Paracentrotus lividus

The growth of the skleleton and changes in biochemical constituents (proteins, carbohydrates and lipids) were observed in embryos (days 0 and 1) and larvae (2-8 days) of the sea urchin Paracentrotus lividus that were starved (C 0) or fed low (1,000 cells of Hymenomonas elongata, C 1) or high (5,000 cells, C 5). Different batches of C 1 and C 5 larvae were fed first the 2nd, 3rd, 4th or 5th day after fertilization. Initiation of feeding 24 h after hatching slowed down the rate of increase in length of the larval appendages. A differential growth of skeletic rods (somatic and postoral rods) and variations in proteins weights shows the existence of a mixotrophic phase between endotrophic and planktotrophic phases. Best development occured in larvae which were first fed at the lower food level 24 h after hatching. On the 2nd and the 3rd day the somatic/postoral rod ratio is ≥1. This higher ration can be used to estimate the age of natural populations of larvae.     

Influence de la 6-benzylaminopurine sur la différenciation plastidiale dans les cotylédons de concombre

Treatment with 6-benzylaminopurine (6-BAP; 10⁻⁵ g/ml) accelerates the growth of detached cucumber cotyledons (Cucumis sativas L.), primarily through an increased water uptake by the tissues. A comparative study of pigment composition and ultrastructure in 6-BAP treated and untreated cotyledons shows that cytokinin, in the presence of light, accelerates the transformation of etioplasts into chloroplasts. 6-BAP also enhances the synthesis of membrane precursors as indicated by the formation of a dense prolamellar body and by the persistence of a pseudo-cristalline structure in 6-BAP treated material. Stimulation of biosynthetic activity by cytokinin leads simultaneously to an increase in the rate of the pigment synthesis and to an acceleration in the building of the lamellar system. Furthermore, chloroplasts of 6-BAP treated cotyledons show abnormal features such as a striking increase in the number of thylacoids per granum and a poor development of the intergranal system.     

Effets de la zearalenone sur la cellule bactérienne

Zearalenone, a macrocyclic lactone, shows a limited antibacterial activity which can be demonstrated in Grampositive spore-forming bacteria. In a sensitive Bacillus thuringiensis (Berliner), the mycotoxin disturbs various bacterial metabolisms: physiological damages (decreased growth rate, inhibition of sporulation and enzyme synthesis) and cellular alterations (filamentous forms or snake-cells) are noted. On the other hand, although zearalenone has been found to give a positive response in the presumptive screening test for mutagens measured by DNA-attacking ability on Bacillus subtilis, this mycotoxin failed to demonstrate mutagenicity in routine test using liver homogenate and Salmonella typhimurium strains.

     

Le système protéolytique de Penicillium roqueforti: II - Purification et propriétés de la protéase acide

An extracellular protease has been isolated from the culture medium of Penicillium roqueforti. The enzyme was purified by precipitation with ammonium sulfate, filtration on Bio-gel P 100 columns and chromatography on D.E.A.E.-cellulose columns The purified preparation was homogenous by gel filtration on Bio-gel P 60 and electrophoretical analysis at pH 9.0 and 5.0.The protease exhibited the properties of an acid protease: the optimum pH was 3.5 for casein or hemoglobin hydrolysis and for bovine trypsinogen activation; at 40°C, the enzyme is most stable in the range of pH 3.5 to 5.5; the optimum temperatures was 50°C.E.D.T.A., D.F.P. and sulfhydryl reagents induced no inhibition.The enzyme exhibited a milk clotting activity that was fifty times weaker that the activity of rennin. Its molecular weight, estimated by gel filtration was 33 400. Amino acid composition is: Lys₁₅, His₂, Arg₁, Trp₅, Asp₃₃, Thr₂₇, Glu₁₆, Pro₁₀, Gly₄₀, Ala₂₅, Cys₂, Val₂₁, Ile₂₀, Leu₂₁, Tyr₁₄, Phe₁₉.The properties of this protease were closely similar to that of P. janthinellum and Aspergillus oryzae.     

Contribution à l'étude de la structure de la chromatine: I - Etude physico-chimique de la stabilité de la chromatine

Physicochemical studies of calf thymus chromatin were performed on micromicellar suspensions by thermal denaturation. These diluted suspensions were obtained, by a controlled shearing method, from a compact gel chromatin. Sedimentation and free-flow electrophoresis determined the size distribution of these particles. The most important result is a new transition on the melting profiles corresponding to a sudden increase of solution turbidity. This chromatin solution transition occurs at a higher temperature than usual DNA transition. The degree of « turbidity transitiondiminishes with micelle size but disappears when they are very mildly degraded by DNAases and when F₁ histone fraction is removed.This transition is not only size dependent but also depends on the micellar structure. This phenomenon is interpreted as an excluded volume effect by contact between compact and native regions of nucleoprotein micelles and denatured coils of DNA. Our study tried to show that the degree of turbidity transition can be a criterion of chromatin native structure.     

La diversité floristique de la végétation psammophile de la région de Tlemcen (nord–ouest Algérie)

This study is devoted to the analysis of the psammophyte of the coastal and semi-continental dunes in Tlemcen. Interesting results have been obtained, in particular, on the biological and ecological aspects of the psammophyte. The interpretation from Factoriel analysis of correspondences enabled us to identify the different phytosociological classes (Cakiletea maritimae, Ammophiletea, Quercetea ilicis, Therobrachypodietea and Stellarietea mediae). Some of these classes (Cakiletea maritimae and Ammophiletea) inhabit, exceedingly well, the embryonic dunes. Some species (Therobrachypodietea) colonize the quickset dunes. Lastly, some others (Quercetea ilicis) settle in the more mature and stable dunes. By using the phytosociological and phytodynamical data, we have been able to understand the vegetation and its diversity. To cite this article: H. Stambouli-Meziane et al., C. R. Biologies 332 (2009).     

Etude de la fertilité des eaux marines au moyen de tests biologiques effectués avec des cultures d'algues. II. Limitation nutritionnelle et viabilité de l'inoculum

Ten cultures of phytoplankters, including four strains of Skeletonema costatum from different origins, were used to improve some aspects of the bioassay technology. Special attention was paid to the preliminary nutrient limitation of the inocula. When the cells are maintained in nutrient starvation, their carbon, nitrogen, carbohydrates, proteins and above all chlorophyll a contents decrease. The minimum appears after a range of 2–7 days, according to species. The survival of these limited cells and their capacity to give rise to active growing cultures when sub-cultured are different with species, but efficiency in the inocula they provide usually can occur only until the minimum content in cellular components appears. Starved cells and enriched cultures of Chaetoceros lauderi and Skeletonema costatum were used to inoculate several samples of sea water, in order to test the effect of the starvation on the experimental results. It appears that the starved cells increase the sensitivity of the method, but they are more susceptible to substances limiting their growth. In the opinion of the authors the best way would be to use both starved and enriched cells as inocula, but, when this is impossible, cautiously starved cells should be used with unpolluted sea waters.     

Role écologique deDigitalis purpurea dans la limitation naturelle des populations du puceron strié de la pomme de terreAulacorthum solani parAphidius urticae dans l'ouest de la France

Résumé En Bretagne les cultures de pommes de terre sont colonisées parAulacorthum solani,kltb,Macrosiphum euphorbiae thomas etMyzus persicae sulz. Lorsque le vol de contamination initiale par A.solani etM. persicae est de grande amplitude, le vol de dissémination est virtuellement absent, et inversement. Nous montrons que ceci est d? au très fort parasitisme qui affecte les populations dès leur installation sur les pommes de terre. En ce qui concerneA. solani, attaqué en particulier parAphidius urticae Hal. le r?le de la digitale en tant que producteur de pucerons et de parasites est mis en évidence. Le synchronisme entre la production de pucerons ailés et de parasites varie selon les biotopes et à ce titre la température para?t avoir une action prédominante.

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Summary In western France, the potato crops are regularly invaded byA. solani kltb,Myzus persicae sulz. andMacrosiphum euphorbiae thomas. Whenever the primary infestation by winged aphids is low, then the dissemination flight is relatively important and conversely (fig. 1). The reason is that aphidiids exert a good control as soon as aphid populations are building up. These parasites may be carried as eggs or young larvae in the alate aphids ofA. solani (table 1) and asD. purpurea constitutes one of its main winter host (A. solani is anholocyclic), the impcrtance of this plant was investigated as regards to aphid, parasite and hyperparasite production.Aphidius urticae hal-was the only parasite recorded so far with five hyperparasite species. On potato plants, too,A. urticae seems specifically concerned withA. solani otherwise attacked byAphidius picipes nees andAphidius ervi hal. It was shown some discrepancies between different biotopes as regards to the rate of parasitism at the same time (table 2) and attention is stressed on apparent differences between parasitization of apterous and winged instars (table 3), the importance of which is discussed regarding to the amount of winged invaders the foxglove may produce by the time the potato plants are shooting. Temperature appears to exert an important r?le in this respect.

     

Rôle de L'éthylène dans L'Accumulation de Capsidiol et la Sensibilité a Phytophthora capsici chez le Piment Traite par un Eliciteur

Role of ethylene in both the synthesis of capsidiol and the susceptibility to Phytophthora capsici of pepper treated with an elicitor With inoculated plants, there is a strong increase of ethylene, specially with Phyo 636. But, with plants inoculated and treated with G5 15 the quantities of ethylene are less important than with those ones inoculated and untreated with G5 15. After contamination (and only in this case), there is capsidiol synthesis as well wit h treated plants as with untreated ones, and the quantities are not significantly different. Generally, the level of induced resistance is higher wit h Phyo 636 (genetically resistant) than with Yolo Wonder (genetically susceptible). The adjunction of ethylene precursor (ACC) to G5 15 elicitor increases induced resistance with Yolo Wonder but decreases with Phyo 636: the inverse effect is observed when using ethylene inhibitor (AVG). It is suggested that, in the interaction Pepper—Phytophthora capsia, neither ethylene production nor capsidiol synthesis can be considered as biochemical tracers of induced resistance.     

Nouvelle découverte dans le Nord-Ouest de Madagascar et répartition géographique des espèces du genre Palaeopropithecus

During the field-work of 2003 in the Narinda peninsula in the Province of Mahajanga (North-West of Madagascar), we found a Palaeopropithecus of large size in the new cave “Raulin Zohy”. This fossil differs in morphology and size from the remains coming from other sites of this area and belonging to a new yet undescribed species. This discovery proves that two species of this genus existed in the costal area of the Province of Mahajanga. This Palaeopropithecus attributed to maximus species allows a reconsideration of the geographical distribution of this subfossil lemur species, and asks an interesting question about the biogeography on the small new species.     

Étude thermodynamique de la transition hélice–pelote statistique en solvants mixtes de différents esters de l'acide poly(L-glutamique)

Helix–coil transition of poly(γ-methyl-L -glutamate), poly(γ-ethyl-L -glutamate), and poly(γ-benzyl-L -glutamate) has been studied in mixed solvents by calorimetry, polarimetry, and viscometry. The experimental data have allowed the evaluation of solvation enthalpy Δh_b, equilibrium constant K for hydrogen bond formation between the active solvent component and CO and NH groups, and the cooperativity parameter σ. The conformational transition of polypeptides in solution in a mixed solvent containing enough active solvent to maintain the coiled conformation has been produced by dilution with the helix-supporting solvent for the measurements of enthalpy of transition Δh_s. The average value for Δh_s is 3550 ± 300 J/mol and is practically independent of the nature of the side chain for the dichloroacetic acid-ethylene dichloride solvent pair at 25°C. A noticeable concentration effect exists in the case of poly(γ-benzyl-L -glutamate). The helical conformation is less stable for poly(γ-ethyl-L -glutamate), and this is explained by a steric effect hindering the access of dichloroacetic acid to side chains. Constant K has been calculated using polarimetric data and also from values of Δh_s obtained at different temperatures using the Bixon and Lifson theory on the one hand and that of Sayama and coworkers on the other hand. Values of σ for poly(γ-ethyl-L -glutamate) have been calculated according to both theories mentioned, and the results show that the two sets of values are quite similar. The constant σ depends on the nature of the active solvent, on temperature, and on the binary-solvent composition. These conclusions are confirmed by viscometric results. Values of Δh_b calculated from constant K are 5230 J/mol when Bixon and Lifson theory is used and 5569 J/mol when the theory at Sayama and coworkers is used. In both cases the value for Δh_b is much lower than that of an intramolecular hydrogen bond. Experimental results suggest that the solvation mechanism would proceed in a manner so that mechanisms described in both theories are involved.     

Activité DNA-polymérase nucléaire dans les spermatozoides de souris et évolution de cette activité au cours de la spermatogenèse

The presence of a nuclear DNA polymerase activity has been demonstrated in the mouse testis by a cytochemical method. The enzyme was present in the nuclei of the various cell types of mouse spermatogenesis, including spermatozoa. The nuclear activity increased during meiotic prophase and then decreased in spermatids and spermatozoa. A peculiar attention was devoted to the properties of the nuclear DNA polymerase present in spermatozoa. All four deoxyribonucleoside-triphosphates were needed for optimal activity; the acid-insoluble radioactive product obtained by polymerization in situ was completely removed by DNase, but not by RNase nor by pronase. The reaction of polymerization was DNA-dependent, sensitive to high concentrations of KCl and not affected by NEM nor by PHMB.     

Modalités de l'inhibition de la croissance et de la synthèse des acides nucléiques des plantules de blé par l'acide abscissique

The growth of wheat seedlings (Triticum sativum) is inhibited by abscisic acid (ABA). The inhibition increases with the concentration of ABA (from 10^-6M to 5 × 10^-5M) and is stronger in the case of coleoptiles and first leaves than in roots. In contrast, naphthaleneacetic acid (ANA), at 10^-5M, exerts its greatest inhibitory effect on the roots. The inhibitory effect of ABA on coleoptiles can be partially overcome by kinetin and to a much smaller degree by gibberellic acid. Neither of these two compounds, at 10^-5M, had any effect on the ABA-induced inhibition of root growth. The RNA and DNA contents per plant organ are considerably reduced after treatment of the seedlings with ABA, particularly in the coleoptiles and the first leaves. The incorporation of uracil-2-¹⁴C and uridine T (G) into RNA of treated seedlings is reduced in the case of coleoptiles and first leaves, but considerably enhanced in roots. The mechanism of the action of ABA is discussed in the light of these results.     

Nouvelles découvertes de dents d’hominidés dans le membre Kaitio de la formation de Nachukui (1,65–1,9 Ma), Ouest du lac Turkana (Kenya)

New hominid teeth from the Kaitio member (1.65–1.9 Myr) in West Turkana (Kenya). New hominid teeth have been recovered from the archaeological sites of Kokiselei 1 and Naiyena Engol 1. These two sites are located in the west side of the Turkana Basin and belong to the Kaitio member of the Nachukui Formation. They are dated between 1.65-1.79 and 1.7-1.8 Myr respectively. The four teeth (left maxillary canine and first molar, right maxillary third molar and left mandibular third molar) discovered in Kokiselei 1 are attributed to Australopithecus boisei. The right mandibular first premolar found in Naiyena Engol 1 is referred to Homo sp. aff. ergaster. To cite this article: S. Prat et al., C. R. Palevol 2 (2003).     

Faunes et paléoenvironnements des principaux sites archéologiques plio-pléistocènes de la formation de Nachukui (Ouest-Turkana, Kenya)

Faunas and paleoenvironments from main archaeological Plio-Pleistocene sites of the Nachukui Formation (West Turkana, Kenya). The Nachukui Formation is currently under archaeological investigation, especially within the Kalochoro (2.35 – 1.9 Myr) and Kaitio (1.9 – 1.65 Myr) Members. Six main archaeological sites have been excavated from this time period, which yield rich vertebrate faunas collected in situ or in close vicinity to the site. Paleontological studies help to precise the specific diversity for each site and increase our documentation for each Member with the discovery of new taxa. They allow to provide new informations about the biotope diversities exploited by Hominids and show a climatic tendency towards more humid environment between the Members. To cite this article: J.-P. Brugal et al., C.R. Palevol 2 (2003).     

Aspects ultrastructuraux et synthèse de la thyroglobouline dans les cultures de thyroides avant et après transplantation chez des rats hypophysectomisés

Two aspects concerning the study of thyroglobulin synthesis and of the ultrastructure of thyroid glands in organotypic cultures have been studied: (1) the chronology of ultrastructural alterations in thyroid cultures leading to the loss of thyroglobulin synthesis; and (2) the role of TSH in the re-establishment of the characteristic features in the cultured cells following transplantation.Alterations of the endoplasmic reticulum start on the very first day of culture. The ribosomes detach themselves from the membranes which then disappear. On the third and fourth day, significant alterations are observed on mitochondria and nuclei. The lysosomes disappear, while the Golgi apparatus is hardly affected.All the above modifications are reversible, since it is possible to re-establish the characteristic features of the endoplasmic reticulum and the synthesis of thyroglobulin after transplantation of the cultured glands into normal animals.The reappearance of phenotypic traits of the thyroid cells can also be obtained after transplantation into hypophysectomized rats. However, the level of thyroglobulin synthesis in these transplants, which is similar to that in the host gland, is lower than in grafts into normal animals.This results shows that TSH is not required for differentiation and for manifestation of the phenotypic traits of the thyroid gland. It seems therefore that the role of TSH is not to stimulate differentiation, but to maintain and regulate the level of specific processes in the already differentiated thyroid cell.     

Les sites archéologiques plio-pléistocènes de la formation de Nachukui, Ouest-Turkana, Kenya : bilan synthétique 1997–2001

Plio-Pleistocene archaeological sites in the Nachukui Formation, West Turkana, Kenya: synthetic results 1997–2001. Stretched along the western side of the Turkana Basin, the Nachukui Formation preserves a large number of Plio-Pleistocene archaeological sites. Research carried out by the WTAP documents hominid behavioral evolution and technical diversity, through a time period ranging from 2.35 Myr to 0.7 Myr and within a relatively precise chronostratigraphic and paleoenvironmental frame. This work is based on comprehensive excavations conducted between 1997 and 2001 at the Late Pliocene and Early Pleistocene site complexes of the formation. To cite this article: H. Roche et al., C.R. Palevol 2 (2003).